Transportation systems which use magnetic fields to provide levitation of a cargo-carrying or passenger-carrying vehicle have been under study and experiment for many years. The IEEE Transactions on Magnetics for September, 1974, pages 397-473, reported on a number of such systems which had been investigated and many of which were under test.
In general, magnetic levitation, sometimes called "maglev", has been of two types. Attractive maglev has used ordinary electromagnets which are attracted to the underside of a ferromagnetic rail without making contact. The magnet current is controlled by solid state amplifiers so as to maintain a clearance gap between the magnet poles and steel rail. Propulsion of levitated vehicles is by linear induction motor or linear synchronous motor.
Repulsion maglev has also been tested. In this form of vehicle levitation, superconducting coils on board the vehicle provide the magnetic field. Lift is produced by repulsion between these superconducting magnets and eddy currents that their moving magnetic fields induce in an aluminum rail structure. The vehicle must be moving at a speed of about twenty miles per hour before the induced eddy currents provide sufficient lift to levitate the vehicle. Obviously, this take-off speed is an objectionable feature of repulsion maglev as is the necessity of packing equipment on board the vehicle to maintain the superconducting condition of the magnet coils.
The use of electromagnets to provide the principal lifting force for a vehicle is at best cumbersome and costly. In my patent application, Ser. No. 151,412, filed May 19, 1980, on which a notice of allowance is pending, I described and claimed a permanent magnet system in which a vehicle is levitated by attraction between a set of permanent magnets in the vehicle and a steel rail above the magnets. Stability is provided by repulsion between a second set of permanent magnets in the vehicle and a rail directly above composed of ceramic magnets with transverse polarity orientation. In such a system strong vertical forces must be quickly applied for both levitation and repulsion in order to counteract both downward drop-out and upward track contact tendencies under changing load and side wind conditions.
The present invention is aimed at a permanent-magnet-levitation system in which vertical movement of a vehicle is inherently stable and horizontal movement is controlled to prevent contact beteen levitation magnets and the track.